Recent improvements in rapid firing weaponry have created complex problems for the fuze designer. Fuze/projectile combinations are subjected to high intensity axial forces caused by ammunition feeding, chambering and firing in addition to the usual centrifugal or spin forces generated by rifled gun barrels. Fuze design is further complicated by consideration of fuze safety. Users are concerned that the fuze not arm before the projectile travels a safe distance downrange after leaving the gun barrel. Electronic timing circuits used to provide the arming function have historically suffered from lack of reliability and are subject to malfunction causing safety type failures. Typical electronic proximity fuze functions require that two modes of target induced detonation be provided; electronic circuits initiate detonation upon approach of the projectile to the target and impact detonation is usually utilized as a second mode for initiating the explosive train. The proximity function is desired to operate in either of two cases. In either case, the primary mode of operation is on impact. However, if the projectile misses the target, the proximity function should operate and if the target is too "soft" to cause primary impact detonation the proximity mode function should provide the secondary form of detonation. Relatively small caliber electronic fuzes severely limit the volume available to implement the safing and arming function within the constraints imposed by applicable military design specifications. Ball rotors and ball driven disk rotors have been used in small projectile fuzes to retard mechanical arming until the projectile has left the gun tube, but the nominal fuze arming time achieved by these methods is, in many instances, significantly less than that desired. In addition, ball driven disk rotors commonly incorporate explosive elements mounted eccentric to the fuze major axis. This latter condition can be the cause of undesirable rotor imbalance and, in some designs, may require the explosive output to be subsequently transferred to the fuze major axis to facilitate booster initiation. This technique occupies precious volume and proliferates the quantity of explosive elements required between the detonator and the booster charge.
Further, in an electronic proximity fuze, the safing system must be designed so as not to interfere with the functions of the foreward located antenna. This consideration generally precludes the use of a temperature or air flow sensor such as a melting link or propellor device as a safety element in the foreward sector of the fuze. Spin detents and setbacks stops have been utilized to prevent this rotation prior to sensing of centrifugal and set back force environments. Ball driven disk rotors have been utilized wherein the disk might take two safe positions before finally arriving at the armed position. This multiple step arming system has the advantage of taking more time thereby providing more safety in the projectile as a result of providing a greater distance from the gun barrel at the time of arming. It is also more likely to fail in a safe position in case of a malfunction; a desirable feature.
Prior art fuze systems may utilize one of several packaging techniques. Typically, the electrical components are mounted, both electrically and mechanically, to small printed circuit boards which, in turn, are interconnected by soldered or welded wires or printed cables. The multitude of electrical and mechanical interconnections in these configurations tend to limit the reliability and even, in extreme cases, the safety of the system. Human error in fabrication of these complex electronic assemblies adds further to reliability and safety problems.
In fuze designs utilizing electronic radiating systems, a significant amount of radiated power is effectively lost in that the radiation; that is, the beam width angle of the radiating element; is not limited adequately to the flight path direction. Radiating beam width angles are increased by uncontrolled radiation from the projectile body in response to excitation from the intended radiating element.
Since the projectiles herein discussed are used in high speed gun systems, it follows that large quantities of them are produced. Threaded parts pose the dual problems of high part manufacturing costs and high assembly costs. Threaded fasteners are relatively expensive to make and to assemble since they do not lend themselves well to automated factory assembly systems.